Transverse oscillations in 3D along Ca II K bright fibrils in the solar chromosphere

Abstract

Fibrils in the solar chromosphere carry transverse oscillations as determined from non-spectroscopic imaging data. They are estimated to carry an energy flux of several ${\mathrm{kW}\mathrm{m}}^{-2}$, which is a significant fraction of the average chromospheric radiative energy losses. We aim to determine oscillation properties of fibrils not only in the plane-of-the-sky (horizontal) direction, but also along the line-of-sight (vertical) direction. We obtained imaging-spectroscopy data in $\mathrm{Fe}\mathrm{I}$, $\mathrm{Ca}\mathrm{II}\mathrm{IR}$, and $\mathrm{Ca}\mathrm{II}\mathrm{K}$ with the Swedish 1-m Solar Telescope. We created a sample of 605 bright $\mathrm{Ca}\mathrm{II}\mathrm{K}$ fibrils and measured their horizontal motions. Their vertical motion was determined through non-LTE inversion of the observed spectra. We determined the periods and velocity amplitudes of the fibril oscillations, as well as phase differences between vertical and horizontal oscillations in the fibrils. The bright $\mathrm{Ca}\mathrm{II}\mathrm{K}$ fibrils carry transverse waves with a mean period of $2.1\times 10^2$s, and a horizontal velocity amplitude of 1${\mathrm{km}\mathrm{s}}^{-1}$, consistent with earlier results. The mean vertical velocity amplitude is 1.1${\mathrm{km}\mathrm{s}}^{-1}$. We find that 77% of the fibrils carry waves in both the vertical and horizontal directions, and 80% of this subsample exhibits oscillations with similar periods in both horizontal and vertical directions. For the latter, we find that all phase differences between $0$ and $2\pi$ occur, with a mild but significant preference for linearly polarized waves (phase difference of $0$ or $\pi$). The results are consistent with the scenario where transverse waves are excited by granular buffeting at the photospheric footpoints of the fibrils. Estimates of transverse wave flux based only on imaging data are too low because they ignore the contribution of the vertical velocity.

arXiv comment12 pages, 12 figures

References in corpus (28)

• CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
• Spectroscopy Made Easy: Evolution
• Numerical simulations of quiet Sun magnetism: On the contribution from a small-scale dynamo
• Numerical simulation of the three-dimensional structure and dynamics of the non-magnetic solar chromosphere
• The formation of the Halpha line in the solar chromosphere
• CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter
• Ubiquitous torsional motions in type II spicules
• On the nature of kink MHD waves in magnetic flux tubes
• Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
• Oscillations and waves in solar spicules
• STiC -- A multi-atom non-LTE PRD inversion code for full-Stokes solar observations
• Flocculent flows in the chromospheric canopy of a sunspot
• Evidence for the photospheric excitation of incompressible chromospheric waves
• DELO-Bezier formal solutions of the polarized radiative transfer equation
• SSTRED: Data- and metadata-processing pipeline for CHROMIS and CRISP
• Transverse oscillations in chromospheric mottles
• On fibrils and field lines: The nature of H$\alpha$ fibrils in the solar chromosphere
• Structure and Dynamics of Isolated Internetwork Ca II H Bright Points Observed by Sunrise
• Fast approximation of angle-dependent partial redistribution in moving atmospheres
• Transverse Wave Induced Kelvin-Helmholtz Rolls in Spicules
• The generation and damping of propagating MHD kink waves in the solar atmosphere
• Transverse Oscillations in Slender Ca II H Fibrils Observed with Sunrise/SuFI
• Three-dimensional modeling of chromospheric spectral lines in a simulated active region
• Kink waves in an active region dynamic fibril
• Polarised kink waves in magnetic elements: evidence for chromospheric helical waves
• Physical properties of bright Ca II K fibrils in the solar chromosphere
• Helical motion of magnetic flux tubes in the solar atmosphere
• Rapid Blue- and Red-shifted Excursions in H$\alpha$ line profiles synthesized from realistic 3D MHD simulations